This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-240009, filed Aug. 26, 1999; and No. 11-240011, filed Aug. 26, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a directional antenna apparatus used in, for example, a base station of a radio communications system for data communications between the base station and a plurality of terminal stations.
In a radio communications system for e.g. mobile communications or indoor radio communications, adaptive array antennas are commonly provided for effective use of the limited frequencies, suppression of the multipath phasing, or elimination of interference waves over a single channel. For example, as disclosed in Jpn. Pat Appln. KOKAI Publication No. 9-219615, an adaptive array transmitting/receiving apparatus equipped with an adaptive array antenna is provided in the base station in a radio communications system for communications between the base station and the terminal stations.
That is, the device disclosed in the publication is structured in the following manner. Amplitudes and phases of transmitted/received signals from a plurality of antenna elements are weighted by a weighting apparatus 2, and transmitting signals from a transmitting/receiving unit 3 for performing modulating/demodulation on signals are split at a divider/adder and amplitudes and phases thereof are weighted at the weighting apparatus 2 so that they are output to the antenna elements 1. Also, an adaptive array transmitting/receiving apparatus for weighting amplitudes and phases of received signals from the antenna elements 1 at the weighting apparatus 2 and combining the weighted signals at the divider/adder 4 to output them to the transmitting/receiving unit 3 is provided at a base station. At a time of providing the base station, reference signals are transmitted to the adaptive array transmitting/receiving apparatus from a direction of desired wave and a direction of undesired wave, a coefficient of weight is calculated at an external calculating device 5 on the basis of the received signals of the reference signals of the adaptive array transmitting/receiving apparatus, and the coefficient of weight is set to the weighting apparatus 2 via an interface 6, so that directional control is performed.
Conventionally, in a case that an adaptive array antenna is employed as an antenna, since a transmitter/receiver for a base station or a terminal station is structured as a base station or a terminal station equipped with an adaptive array transmitting/receiving apparatus at an initial stage of equipment, there does not occur any problem. However, when an adaptive array antenna is intended to be employed for a base station or a terminal station which is equipped with the existing radio device without employing such an adaptive array antenna, there occurs a problem that, since the existing transmitter/receiver of the base station or the terminal station can not be reused as the equipment for the adaptive array antenna, the entire system of the base station or the terminal station must be changed.
It is hence an object of the present invention to provide a directional antenna apparatus which can be easily connected to the existing radio apparatus not employing an adaptive array antenna.
According to the present invention, a directional antenna apparatus having an plurality of antenna elements for controlling the directivity is provided comprising: first receiving frequency converting means for converting the frequency of signals received by the antenna elements; weighting means for weighting on the amplitude and the phase for the signals converted by the first receiving frequency converting means; adding means for adding the weighted signals by the weighting means; and second receiving frequency converting means for converting back the frequency of the added signal to the original frequency of the received signals.
As a result, the directional antenna apparatus of the present invention can easily be connected to an existing radio apparatus, which does not employ an adaptive array antenna.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.